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McQuay OM 751 23
Description of Operation
Unit Mode Priority
The UVC uses the network variables and binary inputs listed in Table 10 and Table 11 to
determine the current unit mode. Special purpose UVC unit modes have higher priority than
the normal UVC unit modes as shown in the tables.
Each table lists the highest priority items on the left to the lower priority items to the right. The
right-most columns indicate unit operation as a result of the left-most columns. The term
“Don’t care” in these tables implies that another network variable or binary input to the left
has a higher priority.
Table 10: Special purpose UVC unit mode priority
Table 11: Normal UVC mode priority
Priority result
Emergency override
input
1
Remote shutdown
binary input
Energy hold
off input
1
Energy hold
off output
2
Unit mode
output
2
Actual UVC action
Normal
3
De-energized
4
Normal Normal
See the normal
UVC mode priority (Table 11)
Energy hold off Energy hold off Off Off
Energized
5
Don’t care Energy hold off Off Off
Pressurize Don’t care Don’t care Don’t care Off Pressurize
De-pressurize Don’t care Don’t care Don’t care Off De-pressurize
Purge Don’t care Don’t care Don’t care Off Purge
Shutdown Don’t care Don’t care Don’t care Off Off
1. Network input.
2. Network output.
3. Normal indicates the UVC power-up condition.
4. De-energized indicates that the contacts connected to this binary input are open.
5. Energized indicates that the contacts connected to this binary input are closed.
Priority result
Application override
input
1
1. Network input.
Unit mode override
input
1
Unit mode output
2
2. Network output.
Normal (Auto)
3
3. Normal (Auto) is the normal UVC power-up state.
Normal (Auto)
3
Heat
Cool
Emergency heat
Heat Heat
Cool Cool
Night purge Night purge
Off Off
Emergency heat Emergency heat
Fan only Fan only
Heat Don’t care Heat
Cool Don’t care Cool
Night purge Don’t care Night purge
Off Don’t care Off
Emergency heat Don’t care Emergency heat
Fan only Don’t care Fan only